From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E42A513C8E8; Tue, 3 Jun 2025 13:19:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748956787; cv=none; b=OzXII4s0dwiLfSMYhUhxKE0BzT4o5fXm0ASiDpQl37X1SMucw7LmFm2tUItG3H5g0oIqqj6qpKBw1tmy/HuVV7YDMTyTFDVAUjQYzH9MHuXLu/Rf5MeguQJ5pgnia44iw7QebZust6ytp13PfrL3f0wW1LwqJizy+xgNdknDMy4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748956787; c=relaxed/simple; bh=4zckt7TbeInVzta8xoxiyPesS/ueBZE4ZUAMclJmViY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mCHpKqV6WAfI2kYpsbfZaNpbIOmvrGuqWDmCoLd0ewu1WsgmEuvi+IWfNqbj5Rgqee8qy6SBCQGXRJVgKYpN0uRxm5Ef+1p3B4yYkgB+Pa0/VImDlXy9Y4oKZK8cyDFkYEnzzzoSmg5M9n6GPgbBFZYBkPXg0di+Cg0uFwbcofw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Zx62paCd; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Zx62paCd" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=IMyZpNPWuRD8Yt0Bj66tbpS5jFHAY+R03rfqd24z1tA=; b=Zx62paCdRIfY0a9wF1dF/rAnNo UiHTftfyE+VGyqJw2HuPeDULbIREjlmcy3gsX/PpD0vl91RQKOjPUf80vBJyOYXNYYOvQWp51X0az 28iNgL0C6G1PkGFGA/O/X50dvI586E5cM6uuXdEeMXCnDiGkmWwz+ybw5XaMPcnF04tWsNM2lhXPL qQG+LPDKpcTmCnzRrFrZvTxc/Z2izJLAJvnUt7mQKGQRrzVCedZELM+5pxIeSGdU09pIPsEZQGote dWu2tqnaHPFjDJdBXCVu3HNouwDQ3iB3IQj5QrXprdLj3shYEHJfcAcfjQwRnVrG5PyT3IByVNWjb lOa4UeiA==; Received: from hch by bombadil.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uMRYI-0000000B0wB-3pbC; Tue, 03 Jun 2025 13:19:38 +0000 Date: Tue, 3 Jun 2025 06:19:38 -0700 From: Christoph Hellwig To: Christian =?iso-8859-1?Q?K=F6nig?= Cc: Christoph Hellwig , wangtao , sumit.semwal@linaro.org, kraxel@redhat.com, vivek.kasireddy@intel.com, viro@zeniv.linux.org.uk, brauner@kernel.org, hughd@google.com, akpm@linux-foundation.org, amir73il@gmail.com, benjamin.gaignard@collabora.com, Brian.Starkey@arm.com, jstultz@google.com, tjmercier@google.com, jack@suse.cz, baolin.wang@linux.alibaba.com, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, bintian.wang@honor.com, yipengxiang@honor.com, liulu.liu@honor.com, feng.han@honor.com Subject: Re: [PATCH v4 0/4] Implement dmabuf direct I/O via copy_file_range Message-ID: References: <20250603095245.17478-1-tao.wangtao@honor.com> <09c8fb7c-a337-4813-9f44-3a538c4ee8b1@amd.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <09c8fb7c-a337-4813-9f44-3a538c4ee8b1@amd.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Tue, Jun 03, 2025 at 03:14:20PM +0200, Christian König wrote: > On 6/3/25 15:00, Christoph Hellwig wrote: > > This is a really weird interface. No one has yet to explain why dmabuf > > is so special that we can't support direct I/O to it when we can support > > it to otherwise exotic mappings like PCI P2P ones. > > With udmabuf you can do direct I/O, it's just inefficient to walk the > page tables for it when you already have an array of all the folios. Does it matter compared to the I/O in this case? Either way there has been talk (in case of networking implementations) that use a dmabuf as a first class container for lower level I/O. I'd much rather do that than adding odd side interfaces. I.e. have a version of splice that doesn't bother with the pipe, but instead just uses in-kernel direct I/O on one side and dmabuf-provided folios on the other.